Can you get the 40 GbE speeds with a Mellanox ConnectX-3 VPI adapter in Ethernet mode or must it be in Infiniband mode? If the latter, can the required subnet manager software run in Linux or a docker?
If the card has the QSFP+ interface - advertised as FDR, it will also do 56GbE
If the card is only QSFP - advertised as FDR10, it will do only 40GbE.
For the SM, as long as it has an interface (real one) connected to the IB fabric, it'll work.
All of the revisions from A2 and up will do that.
Beware of the A1 revision, I have some inbound and I really hope they are not CX2's packaged in CX3 boards.
They did the same with CX2 A0 - those were CX1's.
I'll post more when I have them.